Proteoglycans

• Viscosity and slipperiness
  • Protein core with sulfated GAGs attached
    • GAGs are glycosaminoglycans
    • Bottle brush appearance
    • Pulls water
  • 6 Different GAGs can be components of proteoglycans
    • Hyaluronic acid
      • Exception: isn’t sulfated
    • Aggrecan and Perlecan
      • Peripheral proteins
    • Syndecan and Fibroglycan
      • Integral proteins

Glycoproteins

• Adhesion Molecules
  • Smaller than proteoglycans
  • Branched sugars
• Fibronectin, laminin, tenscin, entactin, nidogen
  • Attach or bind to other molecules in extracellular space, including other glycoproteins
  • Necessary for cell motility

Interstitual Fluid

• Responsible for transport of water and nutrients between blood vessels and parenchyma
• Metabolic support function of connective tissue
• Bound together by proteoglycans and hyaluronic acid
  • Water comes from the blood vessels and moves into extracellular space via hydrostatic pressure
  • Water is continuously in motion between endothelial cells and parenchyma
    • Oncotic pressure pulls water back in from interstitial fluid to blood vessel, working agains hydrostatic pressure
    • Excess fluid is always left in the extracellular space which is picked up by the lymphatic system and dumped in the thoracic duct and in back to the blood system
• Edema
  • Pitting Edema – pushing on it leaves a dent
  • Abnormal buildup of water in extracellular space
  • Causes:
    • Blocked lymphatic vessels – surgery, elephantiasis
    • Blocked venous return – compromised veins, venous thrombosis (clot)
    • Increased vascular permeability – histamine from mast cells, anaphylactic shock
    • Hypertension – due to increased hydrostatic pressure at arterial end of capillary bed
    • Liver disease – insufficient albumin (produced by liver) to pull H2O back into vessel
    • Starvation – causes lack of plasma proteins that results in H2O remaining in extracellular space
    • Myxedema – overproduction of GAG’s during hypothyroidism
      • Mucous edema – doesn’t pit

Basement Membrane

• Light microscopic term
• Found in extracellular space
• Surrounds all cells except connective tissue cells
  • Fixed and wandering cells don’t have basement membranes
  • Epithelium, muscle and nerve had basement membranes
• Can act as a macrocellular sieve

Electron Microscope Level

• Three layers:
  • Lamina Lucida
  • Lamina Densa
    • Made of collagen type IV
  • Lamina Reticularis
    • Fine reticular fibers (type III collagen) attaches to Lamina Densa
• Basal Lamina – Lamina Lucida + Lamina Densa
  • Sometimes defined differently in cells with very reduced lamina lucida
    • e.g. muscle cells, where basal lamina = lamina densa
• Function:
  • Physical attachment
  • Macromolecular filter
• Structure:
  • Integrin proteins from epithelial cell plasma membrane attaches to glycoproteins lamina and fibronectin, and proteoglycan perlecan in the basal lamina